The present application is directed general towards vehicle tire service and inspection systems, and in particular, towards vehicle tire service and inspection systems configured to measure and evaluate acoustical characteristics of a tire during rolling movement of the tire while in loaded contact with a surface.
A vehicle wheel assembly typically consists of a rigid wheel rim adapted for coupling to a wheel end of a vehicle axle, and an inflated tire mounted to the circumference of the wheel rim. When in use on a vehicle, a small portion of the inflated tire, known as the contact patch, is in direct contact with the road or other surface over which the vehicle is traveling. Rotation of the wheel assembly continually moves the tire surface into and out of the contact patch. So long as wheel spin or wheel skid is not present in the vehicle motion, the portion of the tire surface within the contact patch is stationary relative to the road surface.
The continual movement of the tire surface into and out of the contact patch gives rise to a number of events which generate acoustical energy, i.e., noise or mechanical vibrations which produce an audible sound as the wheel assembly rotates in loaded contact with a surface. For example, the weight of the vehicle and/or rotational acceleration typically deforms a tire from a uniformly round shape to one having a flattened portion at the contact patch and a slight bulge at the adjacent tire sidewalls. The continual deformation of the tire structure during rotational movement can generate acoustical energy or harmonic vibrations within the tire interior volume, depending upon the degree of deformation, the speed of deformation, the tire dimensions, and the material composition of the tire itself. For example, low rolling resistance tires, which typically are composed of stiffer rubber compositions, produce greater amounts of acoustical energy (i.e. noise) when compared to traditional tires. Similarly, winter or snow-traction tires often have rubber compositions which are optimized for cold-weather usage, and which can experience significant changes in stiffness in response to external temperatures, varying the audible noise produced by the tire. Another source of acoustical energy is the displacement of air from beneath the tire contact patch as it travels over the road or other surface, as well as the expulsion or other materials from within voids and recesses defined by a tread pattern on the tire surface. For example, when compared with the relatively smooth tread of traditional touring tires, such as shown in FIG. 1, off-road or all-terrain tires employ aggressive tread patterns having larger voids to facilitate traction, as shown in FIG. 2, which can result in increased levels of noise and acoustical energy generation.
Defects in the tire which alter the shape of the tire or the structure of the tire can give rise to harmonic or repeating pulses of acoustical energy as the tire rotates. Similarly, objects embedded in the tire surface or punctures in the tire material can produce pulses of acoustical energy which repeat for each complete rotation of the wheel assembly. Waves of acoustical energy traveling within the internal volume of the tire can constructively and destructively interfere, generating cavitation noise or vibrations as well.
Consumers are often concerned with the level of noise present in a traveling vehicle, and it is well known that at highway speeds, a large percentage of noise in a vehicle cabin is generated by the road noise associated with the vehicle tires. With many different models of tires available to a consumer, it would be useful to provide a consumer with a relative measure of how loud one model of tire may sound relative to another as a vehicle is traveling.
It would further be advantageous to provide a means by which consumer complaints related to excessive tire noise from a vehicle or even a particular vehicle wheel assembly can be evaluated to determine if the noise is due to a defect in the tire or is inherent to the tire itself.
Finally, it would be advantageous to provide a means by which tire acoustical energy (i.e., noise) can be utilized to identify possible defects in a tire assembly which may not otherwise be readily visible or detectable by conventional tire inspection processes.